1. Field of the Invention
The present invention relates to a semiconductor device including a voltage regulator for regulating the voltage to be supplied to its internal circuitry, and a method of testing the device.
2. Description of the Background Art
Generally, a semiconductor device including a voltage regulator includes first logics operating with a power supply voltage VDD, second logics operating with another power supply voltage VCC different from the power supply voltage VDD, and a register for supplying a power-down signal to the voltage regulator, which are integrated into a semiconductor device, the voltage regulator being adapted for regulating the power supply voltage VDD provided to the first logics so as to generate the power supply voltage VCC to supply the latter to the second logics. When the voltage regulator receives the power-down signal transmitted from the register, the regulator suspends its operation, i.e. interrupts supplying of the power supply voltage VCC to the second logics. In the semiconductor device, the first and second logics and the register are connected to a common reset terminal so that it is possible to initialize the first and second logics and the register at substantially the same timing prior to, e.g. the normal operation of the semiconductor device or an operational test for the first and second logics.
In order to confirm the operation of semiconductor devices against variation in power supply within the allowable range thereof during verification and evaluation of the devices in mass fabrication processes in practice, the semiconductor devices also include a test power supply voltage terminal for applying a test power supply voltage VT to the second logics, by use of which a marginal operation test is carried out on the second logics. The test power supply voltage VT is higher or lower than the power supply voltage VCC and supplied to the second logics under the circumstance where output of the power supply voltage VCC in the voltage regulator is discontinued.
A description will be given below of the marginal operation test carried out on the semiconductor device. Prior to the conduct of marginal operation test, the semiconductor device has the first and second logics and the register reset to their initial state by a reset signal supplied to the common reset terminal described above. When the register is placed in its initial state, the register stops outputting the power-down signal whereby the voltage regulator starts its operation, i.e. starts to provide the power supply voltage to the second logics. The semiconductor device then has the register output the power-down signal to the voltage regulator, whereby the voltage regulator stops outputting the power supply voltage VCC and the test power supply voltage VT is supplied from the test power supply voltage terminal to the second logics in order to execute the first test operation for the first and second logics. After the first test operation completed, the test power supply voltage VT ceases to be supplied to the second logics.
In order to continue the marginal operation test, i.e. to conduct second test, the first and second logics and the register are reset again to their initial state by a reset signal. Due to the resetting, the power supply voltage VCC is supplied to the second logics from the voltage regulator. Thus, the semiconductor device has the register output the power-down signal to the voltage regulator so that the output of the power supply voltage VCC from the voltage regulator is halted in the same way as described above. The test power supply voltage VT is then supplied again to the second logics in order to execute the second test operation for the first and second logics. After the completion of the second test operation, the test power supply voltage VT ceases to be supplied to the second logics and the similar processing will be repeated for the following test operations.
Such a semiconductor device including a voltage regulator is disclosed, for example, by Japanese patent laid-open publication No. 2002-111470, in which the output of the voltage regulator is set to its high impedance state so as to conduct the IDDQ testing for detecting leakage current caused by, e.g. a broken gate of a circuit element of the internal logics.
In the above-described conventional semiconductor device, the first and second logics and the register are, however, arranged such that they are reset simultaneously by a reset signal so that when the first and second logics are initialized, the register is also reset simultaneously to discontinue to output the power-down signal, whereby the voltage regulator supplies the power supply voltage VCC to the second logics. As a result, during the marginal operation test, in order to supply the test power supply voltage VT to the second logics, it is necessary to halt the operation of the voltage regulator. In other words, it is necessary to carry out the processing of halting the output of the power supply voltage VCC from the voltage regulator each time the test operations for the marginal operation test are carried out. Moreover, in order that the test power supply voltage VT will not disturb the power supply voltage VCC output from the voltage regulator in the second logics, it is necessary to halt the test power supply voltage VT from being supplied to the second logics. The result is that the marginal operation test tends to be protracted.
For example, if 200 test items are proceeded to for the marginal operation test and it takes, for example, 5 msec in total for each item to process for halting the operation of the voltage regulator, supplying the test power supply voltage VT to the second logics and discontinuing the power supply of the test power supply voltage VT to the second logics before initializing the first and second logics, then the total time period taken for processing all items is equal to 200 [items]×5 [msec ]=1 [sec]. Moreover, in the marginal operation test the device operation is to be checked for a variety of power supply voltage possible in the allowable range. Hence, K different values of the test power supply voltage VT are presupposed where K is an integer equal to or greater than two and represents the number of values of the test power supply voltage VT. If attention is paid to the marginal operation test for a given product under mass fabrication, then the time consumed merely for the above processing is equal to 1 [sec]×K. Turning to the marginal operation test for the totality of the mass fabrication products, the time consumed for the above processing is protracted, thus leading to increased testing costs.